This research program is aimed at elucidating structure function relationships that are responsible for CMTI-V's selective inhibition of trypsin and other serine proteinases such as Factor XII, a blood- coagulation factor (Hageman Factor). In addition, differential interactions that come into play in the enzyme:inhibitor complexes formed by intact CMTI-V and reactive-site hydrolyzed CMTI-V (CMTI-V) with trypsin and Factor XII, will also be characterized. CMTI-V was isolated and characterized for the first time in the PI's laboratory. Its primary structures consisting of 68 amino acid residues including a disulfide bridge, has been determined. In a collaborative effort, CMTI-V has been cloned and overexpressed in Escherichia coli. Furthermore, a mutant has also been prepared (T43A) which shows a reduced level of inhibitory activity toward trypsin. Knowledge gained from our present study may help design better therapeutic strategies for treating blood coagulation disorders.